1. Field of the Invention
This invention relates to method and apparatus for assembling head units, constituted of plural ink jet type head chips arranged onto a frame, and an ink jet output apparatus.
2. Description of Related Art
An ink jet type output method in which an image is formed by discharging ink droplets is currently both quite popular and widely used, since this method results in printers which are quiet and compact. In such ink jet methods, a plurality of head chips having linearly arrayed nozzles for discharging ink is arranged onto a carriage with a fixed space between them, and each color ink is discharged through the corresponding head chip to obtain a color image. In such a color output apparatus, arrival accuracy of ink discharged from each head chip greatly affects image quality. For example, in the case of recording of 360 dpi, each recording pitch is around 70 .mu.m per recording spot. If the line shifts more than a half recording spot, the image quality would be extremely impaired. In particular, it is still quite difficult to produce identical chips, and so slight variations in the chips which arise during chip production may cause the ejected ink to arrive at the recording medium with a slight positional deviation. Accordingly, effective correction of such shifts is required to keep high image quality.
A conventional ink jet output apparatus of a serial type with a carriage mounting plural head chips has corrected such shifts in the following manner. In one method, where the apparatus is built with head chips individually mounted onto the carriage, each head chip's tendency is checked, and the mounting position thereof is adjusted to correct positional shifts of arrival positions of ink. In another method, where the apparatus is built with head chips formed in a united body with an ink cartridge, ink is discharged from the head chips at a time that the apparatus is operated; the arrival positions of ink are measured to provide information to be stored in a memory; and timings of discharging ink are electrically controlled based on the information stored.
Any method described above, however, makes an assembly line of the apparatus complicated and thereby increases production costs. In addition, in the method in which each head chip is adjusted and mounted, special skill is required to replace the heads, so that users can not replace the heads and no one can do maintenance on the apparatus easily. In the method in which positional shifts are electrically adjusted, the apparatus may be formed in a large size, and therefore, the apparatus can not be used for a compact image output apparatus.